A relay system is for smoothly performing communication in a shadow area and to enlarge a cell-coverage capable of providing a service. Particularly, the relay system seeks improvement of communication between a transmitting unit and reception unit. According to a cooperative reception diversity method in the relay system, when a transmitting unit transmits a symbol to a relay unit, a reception unit may overhear the signal and the reception unit may combine the overheard signal with a signal transmitted from the relay station, and thereby can obtain a diversity gain.
The diversity gain which the reception unit in the relay system can obtain may be affected by both channel conditions between the transmitting unit and reception unit, and channel conditions between the relay station and reception unit. A reception reliability of each bit composed of a signal point is affected by a distance between signal points. However, a relay station in a general relay system intactly outputs a received signal as is to a reception unit without converting a signal point of the received signal. Accordingly, the reception unit using the cooperative reception diversity method may receive, from both the transmitting unit and relay station, a signal mapped with a signal point wherein an error occurs in the same bit.